1 //===--------- DefineExternalSectionStartAndEndSymbols.h --------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // Utility class for recognizing external section start and end symbols and
10 // transforming them into defined symbols for the start and end blocks of the
11 // associated Section.
12 //
13 //===----------------------------------------------------------------------===//
14
15 #ifndef LLVM_EXECUTIONENGINE_JITLINK_DEFINEEXTERNALSECTIONSTARTANDENDSYMBOLS_H
16 #define LLVM_EXECUTIONENGINE_JITLINK_DEFINEEXTERNALSECTIONSTARTANDENDSYMBOLS_H
17
18 #include "llvm/ExecutionEngine/JITLink/JITLink.h"
19 #include "llvm/Support/Debug.h"
20
21 #define DEBUG_TYPE "jitlink"
22
23 namespace llvm {
24 namespace jitlink {
25
26 struct SectionRangeSymbolDesc {
27 SectionRangeSymbolDesc() = default;
SectionRangeSymbolDescSectionRangeSymbolDesc28 SectionRangeSymbolDesc(Section &Sec, bool IsStart)
29 : Sec(&Sec), IsStart(IsStart) {}
30 Section *Sec = nullptr;
31 bool IsStart = false;
32 };
33
34 /// Pass implementation for the createDefineExternalSectionStartAndEndSymbols
35 /// function.
36 template <typename SymbolIdentifierFunction>
37 class DefineExternalSectionStartAndEndSymbols {
38 public:
DefineExternalSectionStartAndEndSymbols(SymbolIdentifierFunction F)39 DefineExternalSectionStartAndEndSymbols(SymbolIdentifierFunction F)
40 : F(std::move(F)) {}
41
operator()42 Error operator()(LinkGraph &G) {
43
44 // This pass will affect the external symbols set, so copy them out into a
45 // vector and iterate over that.
46 std::vector<Symbol *> Externals(G.external_symbols().begin(),
47 G.external_symbols().end());
48
49 for (auto *Sym : Externals) {
50 SectionRangeSymbolDesc D = F(G, *Sym);
51 if (D.Sec) {
52 auto &SR = getSectionRange(*D.Sec);
53 if (D.IsStart) {
54 if (SR.empty())
55 G.makeAbsolute(*Sym, orc::ExecutorAddr());
56 else
57 G.makeDefined(*Sym, *SR.getFirstBlock(), 0, 0, Linkage::Strong,
58 Scope::Local, false);
59 } else {
60 if (SR.empty())
61 G.makeAbsolute(*Sym, orc::ExecutorAddr());
62 else
63 G.makeDefined(*Sym, *SR.getLastBlock(),
64 SR.getLastBlock()->getSize(), 0, Linkage::Strong,
65 Scope::Local, false);
66 }
67 }
68 }
69 return Error::success();
70 }
71
72 private:
getSectionRange(Section & Sec)73 SectionRange &getSectionRange(Section &Sec) {
74 return SectionRanges.try_emplace(&Sec, Sec).first->second;
75 }
76
77 DenseMap<Section *, SectionRange> SectionRanges;
78 SymbolIdentifierFunction F;
79 };
80
81 /// Returns a JITLink pass (as a function class) that uses the given symbol
82 /// identification function to identify external section start and end symbols
83 /// (and their associated Section*s) and transform the identified externals
84 /// into defined symbols pointing to the start of the first block in the
85 /// section and the end of the last (start and end symbols for empty sections
86 /// will be transformed into absolute symbols at address 0).
87 ///
88 /// The identification function should be callable as
89 ///
90 /// SectionRangeSymbolDesc (LinkGraph &G, Symbol &Sym)
91 ///
92 /// If Sym is not a section range start or end symbol then a default
93 /// constructed SectionRangeSymbolDesc should be returned. If Sym is a start
94 /// symbol then SectionRangeSymbolDesc(Sec, true), where Sec is a reference to
95 /// the target Section. If Sym is an end symbol then
96 /// SectionRangeSymbolDesc(Sec, false) should be returned.
97 ///
98 /// This pass should be run in the PostAllocationPass pipeline, at which point
99 /// all blocks should have been assigned their final addresses.
100 template <typename SymbolIdentifierFunction>
101 DefineExternalSectionStartAndEndSymbols<SymbolIdentifierFunction>
createDefineExternalSectionStartAndEndSymbolsPass(SymbolIdentifierFunction && F)102 createDefineExternalSectionStartAndEndSymbolsPass(
103 SymbolIdentifierFunction &&F) {
104 return DefineExternalSectionStartAndEndSymbols<SymbolIdentifierFunction>(
105 std::forward<SymbolIdentifierFunction>(F));
106 }
107
108 /// ELF section start/end symbol detection.
109 inline SectionRangeSymbolDesc
identifyELFSectionStartAndEndSymbols(LinkGraph & G,Symbol & Sym)110 identifyELFSectionStartAndEndSymbols(LinkGraph &G, Symbol &Sym) {
111 constexpr StringRef StartSymbolPrefix = "__start_";
112 constexpr StringRef EndSymbolPrefix = "__stop_";
113
114 auto SymName = Sym.getName();
115 if ((*SymName).starts_with(StartSymbolPrefix)) {
116 if (auto *Sec = G.findSectionByName(
117 (*SymName).drop_front(StartSymbolPrefix.size())))
118 return {*Sec, true};
119 } else if ((*SymName).starts_with(EndSymbolPrefix)) {
120 if (auto *Sec =
121 G.findSectionByName((*SymName).drop_front(EndSymbolPrefix.size())))
122 return {*Sec, false};
123 }
124 return {};
125 }
126
127 /// MachO section start/end symbol detection.
128 inline SectionRangeSymbolDesc
identifyMachOSectionStartAndEndSymbols(LinkGraph & G,Symbol & Sym)129 identifyMachOSectionStartAndEndSymbols(LinkGraph &G, Symbol &Sym) {
130 constexpr StringRef StartSymbolPrefix = "section$start$";
131 constexpr StringRef EndSymbolPrefix = "section$end$";
132
133 auto SymName = Sym.getName();
134 if ((*SymName).starts_with(StartSymbolPrefix)) {
135 auto [SegName, SecName] =
136 (*SymName).drop_front(StartSymbolPrefix.size()).split('$');
137 std::string SectionName = (SegName + "," + SecName).str();
138 if (auto *Sec = G.findSectionByName(SectionName))
139 return {*Sec, true};
140 } else if ((*SymName).starts_with(EndSymbolPrefix)) {
141 auto [SegName, SecName] =
142 (*SymName).drop_front(EndSymbolPrefix.size()).split('$');
143 std::string SectionName = (SegName + "," + SecName).str();
144 if (auto *Sec = G.findSectionByName(SectionName))
145 return {*Sec, false};
146 }
147 return {};
148 }
149
150 } // end namespace jitlink
151 } // end namespace llvm
152
153 #undef DEBUG_TYPE
154
155 #endif // LLVM_EXECUTIONENGINE_JITLINK_DEFINEEXTERNALSECTIONSTARTANDENDSYMBOLS_H
156